A
ccording to a report published in
April by the Greater London
Authority, there are over
1.5 million m^2 of green roofs in London,
and there is a raft of reasons why. Green
roofs offer a host of environmental benefits
including, reducing storm water run-off,
increasing biodiversity, cooling buildings
and their surroundings as well as improving
water and air quality. There is also a
growing body of evidence that shows how
they positively contribute to wellbeing, by
offering views of nature or by providing an
amenity such as a roof garden.
Following the growth of green roofs
comes a rise in ‘blue roofs’ – which retain
water – too, often with the two types
combined. As more planners demand
sustainable urban drainage systems (SuDS),
blue roofs offer a way to release the
rainwater more slowly, avoiding the risk of
over-burdening drainage systems and
causing flooding.
In London, as in other cities around the
world, planning policy is driving the trend
for roofs that do more. In 2008, London’s
mayor published a guide on living roofs
and walls to complement its London Plan.
By 2016, over 40 per cent of the UK’s green
roofs were in the capital. In 2014, current
Mayor Sadiq Khan improved on this by
declaring his intention to make the capital a
National Park City, with green roofs part of
the urban greening plan.
Other UK towns and cities are following
London’s lead. For instance, Cambridge
City Council is developing a green roof
policy as part of its local plan to increase
sustainability. And Leicester’s green
infrastructure strategy includes plans
to encourage more green roofs on both
new-build and refurbishment projects.
Yet green roof types, while well
established, present design challenges to
the specifier and it would be beneficial to
up skill in this field – most accessibly
through CPD training such as thatprovided by BMI UK & Ireland.
There are structural implications when
adding a green or blue roof to a building. A
blue roof, for instance, at capacity would
add around 1 kN/m^2 to the loading. New
buildings can be designed accordingly but
care must be taken with retrofits.
Though green roofs and their design are
well documented, there is less guidance on
the design of blue roofs, other than that
published by the NFRC. However,
BS 6229:2018 ‘Flat roofs with continuously
supported flexible waterproof coverings –The demand for green roof technologies is ramping up, yet they are complex structures
that require understanding; luckily a range of information sources are available to
architects and specifiers. Amanda de Sousa of BMI UK & Ireland explains moreUnderstanding green roofs
Though blue and green
roofs add extra dimensions
to the uses and value of
roofs, they also require an
additional dimension of
care with respect to roof
design, installation and
quality controlSTRUCTURAL ELEMENTS 57ADF NOVEMBER 2019 WWW.ARCHITECTSDATAFILE.CO.UK
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